Http4s improperly parses User-Agent and Server headers
Impact
The User-Agent and Server header parsers are susceptible to a fatal error on certain inputs. In http4s, modeled headers are lazily parsed, so this only applies to services that explicitly request these typed headers.
v0.21.x
val unsafe: Option[`User-Agent`] = req.headers.get(`User-Agent`)v0.22.x, v0.23.x, v1.x
val unsafe: Option[`User-Agent`] = req.headers.get[`User-Agent`]
val alsoUnsafe: Option[`Server`] = req.headers.get[Server]Patches
Fixes are released in 0.21.34, 0.22.15, 0.23.17, and 1.0.0-M38.
Workarounds
Use the weakly typed header interface
v0.21.x
val safe: Option[Header] = req.headers.get("User-Agent".ci)
// but don't do this
val unsafe = header.map(_.parsed)v0.22.x, v0.23.x, v1.x
val safe: Option[Header] = req.headers.get(ci"User-Agent")Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Java / Kotlin (Maven) | org.http4s:http4s-core | >= 1.0.0-M1, <= 1.0.0-M30 | no fix |
| Java / Kotlin (Maven) | org.http4s:http4s-core_2.10 | >= 0.1.0, <= 0.9.3 | no fix |
| Java / Kotlin (Maven) | org.http4s:http4s-core_2.11 | >= 0.1.0, <= 0.21.0-M1 | no fix |
| Java / Kotlin (Maven) | org.http4s:http4s-core_2.12 | >= 0.1.0, < 0.21.34, >= 0.22.0, < 0.22.15, >= 0.23.0, < 0.23.17 | 0.21.34, 0.22.15, 0.23.17 |
| Java / Kotlin (Maven) | org.http4s:http4s-core_2.13 | >= 0.1.0, < 0.21.34, >= 0.22.0, < 0.22.15, >= 0.23.0, < 0.23.17, >= 1.0.0-M1, < 1.0.0-M38 | 0.21.34, 0.22.15, 0.23.17, 1.0.0-M38 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-20- Platform
- Java / Kotlin (Maven)
- Package
org.http4s:http4s-core, org.http4s:http4s-core_2.10, org.http4s:http4s-core_2.11- Disclosed
- 06.01.2023
- Updated
- 11.10.2026 12:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-54w6-vxfh-fw7f - CC BY 4.0
Vulnerability history: org.http4s:http4s-core
All published vulnerabilities of this package (Java / Kotlin (Maven)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 2
- First → latest
- 05.2021 01.2023
- Without a fix
- 1
- Exploited in attacks
- 0
Severity breakdown
- High 1
- Medium 1
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 1
- 2024: 0
- 2025: 0
- 2026: 0
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Http4s improperly parses User-Agent and Server headers this entry
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